Description

In a
practical sense, the minicomputer age began in 1964 with the
Digital Equipment Corporation's introduction of the PDF 8. Potential com-
puter users who had been unable to afford a $500,000 machine found that
for the then
remarkably low price of $27,000 they could purchase a general
purpose computer, limited in power, to be sure, but nonetheless a real
computer. The price was achieved by a combination of several factors: a
simple, classical, no-frills, logical design; a superior packaging technique for the
electronic circuits; and, most
important, use of a short word length. Most of
the
large computers of that era were using word lengths ranging from about
30 to 50 bits, the length being influenced by considerations of accuracy and
instruction format.
By cutting the word length to 12 bits, DEC was able to
greatly reduce the hardware needed in the arithmetic unit. A short word
length limits neither accuracy nor type of operations performed, but it often
means that computation proceeds more slowly. For example, numerical com-
putations may require cumbersome multiple precision routines in order to
secure
adequate accuracy. In simple terms, short word machines achieve low
hardware costs at the
expense of execution efficiency. Since there are many
applications in which the slowest computer is still much faster than the
application requires (e.g., a computer controlling a lathe) the loss of execution
efficiency may not be important.

Issue Date:

1974

Publisher:

Graduate School of Library Science. University of Illinois at Urbana-Champaign